1. Field of the Invention
The present invention relates to an adhesive and, more particularly, to a latent hardener used for an adhesive by which semiconductor chip and TCP (tape carrier package) are connected to substrates by means of a thermal compression bonding.
2. Description of Related Art
Adhesives containing an epoxy resin as a thermosetting resin have been conventionally used in connecting semiconductor chips onto a substrate or in manufacturing of electric apparatuses by connecting TCP to LCD (liquid crystal display)
The reference numeral 111 in FIG. 7A shows an LCD, and the LCD 111 has a glass substrate 112 and ITO (indium tin oxide) electrodes 113 arranged on the glass substrate 112. In connecting the LCD 111 to a TCP which will be mentioned later, an adhesive is firstly applied on the surface of the side to which the ITO electrodes 113 of the LCD 111 are arranged. The reference numeral 125 in FIG. 7B shows an adhesive applied on the LCD 111.
The reference numeral 115 of FIG. 7C shows a TCP, and the TCP 115 has a base film 116 and metal wirings 117 arranged on the surface of the base film 116. The side on which the metal wirings 117 of the TCP 115 are arranged is disposed to an adhesive 125 on the LCD 111, and after being positioned, the side to which the metal wirings 117 of the TCP 115 are arranged is pushed to the adhesive 125.
When heated as pushed in such a state, the adhesive 125 softens, and the metal wirings 117 push away the softened adhesive 125, thereby attaching to the surface of the ITO electrodes 113.
A hardener such as imidazole polymerized of an epoxy resin by heating is generally added to the adhesives mentioned as above, and when heating is further continued in a state where the metal wirings 117 are attached to the ITO electrodes 113, the epoxy resin is polymerized by a catalytic reaction of the hardener to harden the adhesive 125.
The reference numeral 101 of FIG. 7C shows an electric apparatus in a state where the adhesive 125 is hardened. In the electric apparatus 101, the TCP 115 and the LCD 111 are fixed by the hardened adhesive 125 while the metal wirings 117 are attached to the electrodes 113. Accordingly, the TCP 115 and the LCD 111 are connected to each other electrically and mechanically.
However, when the above adhesive is hardened, it is necessary to heat the adhesive at the temperature of as high as not lower than 180xc2x0 C. and, if the pattern of the metal wiring 117 is fine, there may be the case where deformation such as elongation or warp is resulted in the TCP 115 upon heating. Such a problem may be solved when heating temperature is lowered, but time required for the heating treatment becomes longer and productivity lowers.
With regard to adhesives having excellent hardening property at low temperature, some adhesives including radically polymerizable resins such as acrylate and a radical polymerization initiator have been developed in recent years, but such adhesives are inferior in electric characteristics and heat resistance in a hardened state to an adhesive using an epoxy resin.
The present invention has been created for solving the above-mentioned inconveniences in the prior art, and its object is to provide an adhesive able to be hardened under the condition of lower temperature and short time and also has excellent preserving property.
The inventor of the present invention paid his attention to a means where commonly used hardeners are not used but an epoxy resin is subjected to a cationic polymerization and carried out repeated investigations and, as a result, he has found a method where a silane compound having at least one alkoxy group in a structure (a silane coupling agent) and a metal chelate (or a metal alcoholate) are added to an adhesive and the epoxy resin is polymerized (cationically polymerized) by cation produced by the reaction of the metal chelate or the metal alcoholate with the silane coupling agent.
The step of hardening of the epoxy resin by an adhesive to which metal chelate and silane coupling agent are added will be illustrated by the following reaction formulae (1) to (4). 
As shown in the reaction formula (1), a silane compound having at least one alkoxy group reacts with water in the adhesive whereupon the alkoxy group is hydrolyzed to give a silanol group.
When the adhesive is heated, the silanol group reacts with metal chelate such as aluminum chelate and the silane compound is bonded to the aluminum chelate (the reaction formula (2) ).
After that, as shown in the reaction formula (3), another silanol remaining in the adhesive in an equilibrium reaction is arranged to the aluminum chelate to which the silanol is bonded whereupon Bronsted acid points are produced and, as the reaction formula (4) shows, an epoxy ring located at the end of the epoxy resin is opened by the activated proton and is polymerized with an epoxy ring of another epoxy resin (cationic polymerization). As such, when a silane coupling agent and a metal chelate are added to an adhesive, a thermosetting resin such as epoxy resin is cationically polymerized. Since the reactions as shown by the reaction formulae (2) to (4) proceed at lower temperature than the temperature (180xc2x0 C. or more) at which the conventional adhesives are hardened, the adhesive as mentioned above hardens at lower temperature within shorter time than in the case of the conventional ones.
However, when metal chelate or metal alcoholate is directly dispersed in an adhesive with a silane coupling agent, polymerization reaction of an epoxy resin proceeds even at ambient temperature and, therefore, preserving property becomes poor. When metal chelate is sealed in a capsule to prepare the so-called latent hardener, preserving property of the adhesive is enhanced but, when the mechanical strength of the capsule is weak, the capsule may be broken during the step of dispersing the latent hardener in the epoxy resin.
When the present inventor has carried out further and intensive investigations for a method of enhancing the mechanical strength of capsules, it has been found that, where a capsule is constituted using a resin component having a substituent such as hydroxyl group and carboxyl group, metal chelate and the said substituent are connected on the surface part of the hardener particles whereupon the mechanical strength of the capsule becomes high, thereby producing a latent hardener strong against physical impacts.
The present invention has been constituted on the basis of the above-mentioned findings. A latent hardener according to the present invention includes a hardener particle mainly including either or both of metal chelate and metal alcoholate; and a capsule covering the surface of the hardener particle and including a resin component having a substituent of either hydroxyl group or carboxyl group or having substituents of hydroxyl group and carboxyl group. In the latent hardener according to this invention, the substituent or substituents of the resin component react with either or both of the metal chelate and the metal alcoholate on a surface of the hardener particle.
According to an embodiment of the invention, the metal chelate is made of aluminum chelate, where the metal alcoholate is made of aluminum alcoholate. The resin component is also mainly comprises including polyvinyl alcohol.
In another aspect of this invention, a manufacturing method for a latent hardener including a hardener particle and a capsule covering a surface of the hardener particle, includes the steps of: manufacturing a capsule material made of a resin component having a substituent of either hydroxyl group or carboxyl group or having substituents of hydroxyl group and carboxyl group and formed in a powder shape having a smaller average particle size than that of the hardener particle; and forming a capsule in adhering the capsule material on the surface of the hardener particle and melting the capsule material at a state that the capsule material is being adhered on the surface of the hardener particle.
According to a preferred embodiment of the invention, the step of the forming a capsule has a mixing step where the hardener particle and the capsule material are mixed so that the capsule material is adhered on the surface of the hardener particle and a stirring step where the hardener particle in a state of being adhered with the capsule material are stirred so that the capsule material is melted. The ratio of the average particle size of the hardener particle to the average particle size of the capsule material is 100:80 or more, and preferably, 100:50 or more. After the capsule is formed, the capsule and the hardener particle are heated.
In another aspect of the invention, an adhesive includes a thermosetting resin, a silane coupling agent and a latent hardener as mentioned above.